Controlled irrigated catheter ablation systems and methods thereof

ABSTRACT

The present invention relates to open irrigated catheter ablation systems and methods used in connection with open irrigated catheter systems. The systems and related methods can control irrigation fluid flow to obtain temperature responses indicative of temperatures associated with an ablation procedure. Embodiments of the present invention provide irrigated catheter ablation systems having controlled irrigation fluid flow that can be directed at target areas where coagulation is more likely to occur to help minimize blood coagulation and associated problems. The irrigated fluid flow may be regulated in connection with an established or predetermined temperature threshold to improve or better optimize cooling and ablation properties of the system. In embodiments, irrigation flow may be either delayed or intermitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/345,975, filed 30 Dec. 2008 (the '975 application). The '975application is hereby incorporated by reference as though fully setforth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention relates to irrigated catheter assembly systems andmethods for ablating tissue using controlled irrigation flow. Thepresent invention further relates to open irrigated catheter ablationsystems having irrigation fluid flow that may be regulated in connectionwith a predetermined temperature threshold.

b. Background Art

Electrophysiology catheters are used for an ever-increasing number ofprocedures. For example, catheters are used for diagnostic, therapeutic,and ablative procedures, to name just a few procedures. Typically, acatheter is manipulated through the patient's vasculature to an intendedsite, for example, a site within the patient's heart. The cathetercommonly carries one or more electrodes, which may be used for ablation,diagnosis, and/or other treatments.

There are a number of methods used for ablation of desired areas,including for example, radiofrequency (RF) ablation. RF ablation isaccomplished by transmission of radiofrequency energy to a desiredtarget area through an electrode assembly to ablate tissue at a targetsite. Because RF ablation may generate significant heat, which if notcontrolled could result in tissue damage, such as steam pop, tissuecharring, and the like, it is often desirable to include a mechanism toirrigate the target area and the device with biocompatible fluids, suchas saline solution. The use of fluid irrigated ablation catheters canalso prevent the formation of soft thrombus and/or blood coagulation.

Generally, there are two classes of irrigated electrode catheters, openand closed irrigation catheters. Closed ablation catheters can circulatea cooling fluid within the inner cavity of the ablation electrode. Openablation catheters can deliver the cooling fluid through open outlets oropenings on the surface of the electrode. Open ablation catheters usethe inner cavity of the electrode, or distal member, as a manifold todistribute saline solution (or other irrigation fluids known to thoseskilled in the art) to one or more passageways that lead toopenings/outlets provided on the surface of the electrode. The salinethus flows directly through the outlets of the passageways onto or aboutthe distal electrode member. This direct flow through the distalelectrode tip lowers the temperature of the distal tip during operation,which may make accurate monitoring and control of the ablation processsomewhat more challenging.

While open irrigated ablation catheters may improve the safety of RFcatheter ablation by preventing protein aggregation and bloodcoagulation through the dissipation of heat by providing fluid to thesite during the ablation procedure, direct contacting fluid irrigationhas the tendency to cool the electrode temperature dramatically duringablation procedures. The irrigation fluid flow ultimately cuts off theelectrode temperature from rising, which may result in increased (andpossibly more than desirable) ablation in a target area. As such, it canbe desirable to control and more accurately monitor the temperature ofan electrode performing ablation.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to improved open irrigated catheterablation systems and methods used in connection with open irrigatedcatheter systems. Among other things, systems and related methods areprovided that can control irrigation fluid flow and obtain an effectivetemperature response with respect to an ablation procedure. Embodimentsof the present invention provide an irrigated catheter ablation systemhaving controlled irrigation fluid flow directed at target areas, forexample, where coagulation is more likely to occur so as to minimizeblood coagulation and associated problems. The irrigated fluid flow maybe regulated in connection with a predetermined temperature threshold toimprove or better optimize cooling and ablation properties associatedwith the system.

The present invention provides an ablation system having an openirrigated ablation electrode coupled to or connected with a cathetershaft forming an open irrigated catheter assembly in connection with afluid source, an energy source, and a temperature control mechanism forregulating irrigation fluid flow within the catheter shaft assembly.

The present invention further discloses an ablation system having anopen irrigated ablation catheter assembly including an open irrigatedablation electrode coupled to or connected to a catheter shaft formingthe open irrigated catheter assembly in connection with a fluid source,an energy source, such as, for example, radio frequency (RF) generator,and a processor for regulating the temperature control of the electrodeperforming the ablation.

The present invention provides a method of controlling the irrigation ofbiological tissue. The method includes the steps of providing anirrigated catheter ablation system including an irrigated ablationcatheter assembly, a fluid source connected to the catheter assembly, anenergy source connected to the catheter assembly; and an irrigationtemperature control mechanism in communication with the fluid source andenergy source; presetting a temperature threshold for the system thatregulates irrigation fluid flow from the passageway of the catheterassembly; positioning the irrigated electrode of the irrigated ablationcatheter assembly at a target location; applying energy from the energysource to the target location through the irrigated electrode;collecting temperature measurements from a thermal sensor disposedwithin the irrigated electrode; irrigating the ablation electrodeforming an irrigation flow through the passageway of the electrode; andcompleting the application of energy to the target location to form anablation lesion.

The invention further contemplates alternate methods for irrigatingbiological tissue, including a delayed irrigation method and anintermitted irrigation method. The delayed irrigation method involvescollecting temperature measurements of the open irrigation electrodeuntil the collected temperature measurements of the electrode reach apredetermined upper temperature threshold. Once the upper temperaturethreshold is met, the irrigation fluid flow from the passageways of theopen irrigation electrode increases from a maintenance flow rate to anamplified irrigation flow rate. The increased irrigation flow continuesuntil the ablation is completed. In comparison, during the intermittedirrigation method, once the irrigation fluid flow from the passagewaysof the open irrigation electrode is increased, the intermitted methodfurther includes collecting temperature measurements of the electrodeuntil the temperature measurements of the electrode reach apredetermined lower temperature threshold. Once the electrodetemperature measurements reach the lower threshold level, the irrigationflow is reduced to the maintenance flow level through the passageway ofthe electrode. Once the irrigation flow is reduced, temperaturemeasurements continue to be collected from a thermal sensor disposedwithin the irrigated electrode until the temperature measurements onceagain return to the predetermined upper temperature threshold. Theirrigation fluid flow is then increased again through the passageway ofthe electrode therein creating an intermitted irrigation cycle.Accordingly, the irrigation flow is reduced periodically during theintermitted irrigation cycle in response to the temperature. Theintermitted irrigation cycle is continued until the ablation iscomplete. The intermitted irrigation method further provides that theirrigation may be turned off periodically during the ablation procedureto check the temperature response of the electrode until the ablation iscompletely.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an ablation electrode according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view of an ablation electrode of the typegenerally shown in FIG. 1;

FIG. 3 is a cross-sectional view of an ablation electrode according toanother embodiment of the present invention;

FIG. 4 is an isometric view of an ablation catheter system according toan embodiment of the present invention, the illustrated system includingan irrigated catheter assembly operably connected to an energy sourceand a fluid source;

FIG. 5 is an isometric view of an ablation catheter system according toanother embodiment of the present invention, the illustrated systemincluding an irrigated catheter assembly operably connected to an energysource, a fluid source, and a processor;

FIG. 6 is a graphical representation of a conventional tip electrodetemperature response and irrigation flow according to the prior art;

FIG. 7 is a graphical representation of the tip electrode temperatureresponse and delayed irrigation flow rate according to an embodiment ofthe present invention; and

FIG. 8 is an graphical representation of the tip electrode temperatureresponse and intermitted irrigation flow according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the instant invention relates to irrigated catheter ablationsystems and to methods of using irrigated catheter ablation systems. Forpurposes of this description, similar aspects among the variousembodiments described herein will generally be referred to by the samereference number. As will be appreciated, however, the structure of thevarious aspects may differ among various embodiments.

Open irrigated catheter ablation systems of the present inventioninclude an irrigated ablation catheter assembly 10, as generally shownin FIG. 1. The illustrated irrigated ablation catheter assembly 10includes an ablation electrode 12. While embodiments of the inventiondisclosed herein may describe RF ablation catheter assemblies andrelated systems, the invention is not so limited, and the invention mayinclude or involve other types of ablation electrodes and assemblies inwhich the temperature of the device and a targeted tissue area may befactors during the procedure. FIGS. 2 and 3, discussed in further detailbelow, illustrate specific open irrigated ablation electrodes 10according to alternate embodiments associated with the presentinvention. Moreover, FIGS. 4 and 5, discussed in further detail below,illustrate catheter ablation systems embodying features associated withthe present invention.

Embodiments of open irrigated catheter ablation systems in accordancewith the present invention include an open irrigated catheter assembly10 having an open irrigated electrode 12 configured to control the flowof irrigation fluid to an ablation site. The present inventionencompasses irrigated catheter assembly systems that control andregulate the irrigation fluid flow to an ablation site, for example, toimprove or optimized ablation on a tissue while irrigating the surfaceof the tissue. The system may be configured and/or regulated to provideeither intermitted irrigation fluid flow throughout the ablationprocedure or a delayed onset of irrigation to ensure good physicalcontact of electrode 12 with the ablation site. In embodiments,temperature feedback may be used in combination with responsiveirrigation flow to improve or optimize tissue ablation when usingconvention open irrigated ablation catheters to perform an ablationprocedure or technique on biological tissue. Such conventionalirrigation catheters include, but are not limited to, those such as IBITherapy™ Cool Path™ Ablation Catheter available from Irvine Biomedical,Inc.

In particular, one embodiment of the present invention provides a systemand related method for performing RF ablation that includes the delayedonset of the irrigation fluid flow to electrode 12. The onset oftherapeutic irrigation fluid flow may be controllably delayed untilelectrode 12 reaches a predetermined temperature threshold, such as,without limitation, about 65 degrees Celsius. With such embodiments,after electrode 12 reaches the temperature threshold level, theirrigation fluid flow can be started to provide cooling to theelectrode. The delayed onset of the irrigation flow better ensures thatan accurate temperature reading of the electrode may be obtained duringthe initial ablation procedure, which further helps ensure improvedphysical contact between electrode 12 and a targeted site (e.g.,targeted tissue). On the other hand, if the temperature threshold is notmet upon the application of the ablation energy or shortly thereafter,electrode 12 may need to be repositioned to ensure sufficient or properphysical contact with targeted tissue. Since the temperature thresholdis generally set below an associated safety limit, e.g., about 65degrees C., heat related coagulum that is present can be eliminated inconnection with the ablation.

An alternate embodiment of the present invention provides a system andrelated method for performing ablation, such as RF ablation, thatincludes intermitted fluid irrigation flow such that irrigation fluidmay be regulated (i.e., increased and decreased) in response to thetemperature of electrode 12. More particularly, the intermitted fluidirrigation flow may be controlled by a predetermined temperaturethreshold, such as, for example, about 65 degrees. Accordingly, theirrigation fluid flow may be increased when the electrodes reaches about65 degrees and is then decreased once a reduced temperature threshold isreached, such as, for example about 40 degrees. The irrigation fluidflow may be provided for a fixed intermitted duration (i.e., forexample, a fixed period of time), a variable intermitted duration thatis based solely on temperature threshold levels, or some combination ofthe foregoing.

As noted, open irrigated catheter assemblies may be used for a varietyof treatments and procedures. FIG. 1 is an isometric view of part of anembodiment of an irrigated ablation catheter assembly 10. The irrigatedablation catheter assembly 10 includes an open irrigated ablationelectrode 12 connected to a catheter shaft 14 having at least one fluiddelivery tube 16 therein. The ablation electrode 12 includes an outerbody portion 18 having an outer surface 20, and includes a proximalportion 22 and a distal portion 24. As further illustrated in FIGS. 2and 3, electrode 12 of the catheter assembly 10 may further include aninner cavity 26 that may be coupled to or is in fluid communication withfluid delivery tube 16. The open irrigated electrode 12 further includesat least one fluid or irrigation passageway 28 that extends from innercavity 26 to outer surface 20 of electrode 12.

Electrode 12 may be comprised of any electrically, and potentiallythermally, conductive material known to those of ordinary skill in theart for delivery of ablative energy to target tissue areas. Examples ofelectrically conductive materials include gold, platinum, iridium,palladium, stainless steel, and mixtures thereof. A portion of electrode12 may be configured to connect to (or be received by) catheter shaft 14of catheter assembly 10 therein coupling electrode 12 to form anembodiment of a catheter assembly 10. It is noted that alternateconfigurations may be employed with other embodiments in which anelectrode may be comprised of multiple members that connect or fittogether to form the electrode. Various materials may be used in theformation of such electrodes, including a combination of electricallyconductive materials and materials that are less thermally conductive.

In the illustrated embodiment, outer body portion 18 of electrode 20,which includes outer surface 20, is generally cylindrical in shape andterminates in a hemispherical end. However, outer body portion 18 may beprovided in alternate configurations that may be directed to the designof the catheter assembly and/or the procedures being performed. Proximalportion 22 of electrode 12 is generally adjacent to catheter shaft 14,and may be disposed on the distal end of catheter shaft 14. Distalportion 24 of electrode 12 is generally more remote from catheter shaft14 and includes the portion of electrode 12 intended to come intooperative contact with tissue. Distal portion 24 further includes adistal end 36 which may be generally hemispherical, although othershapes and configurations are also contemplated by the presentinvention.

Proximal portion 22 of electrode 12 may further include a mountingportion, such as mounting shaft 34 that is provided on or in connectionwith the proximal end 30 of electrode 12. Mounting shaft 34 may beconnected to or an integral part of proximal end 30 of proximal portion22 of electrode 12 and may be received within or otherwise connected tocatheter shaft 14 of assembly 12. In an embodiment, coupling member 32is disposed between mounting shaft 34 and catheter shaft 14. A couplingmember 32, such as a seal or adhesive, is provided to ensure thatelectrode 12 is connected to catheter shaft 14. Coupling member 32 isgenerally known in the art and includes any type of material known forsuch a purpose to those of ordinary skill in the art. Moreover, couplingmember 32 may have alternate configurations or arrangements to connectelectrode 12 with catheter shaft 14.

Electrode 12 may further include a temperature or thermal sensor 40(generally represented in FIGS. 2 and 3) positioned within distalportion 24 of electrode 12. Thermal sensor 40 may be configured andpositioned to provide improved or optimized accurate temperature sensingby electrode 12 as ablative energy is applied by catheter assembly 10. Alead wire 42 may be coupled to thermal sensor 40 and may extend alongthe catheter assembly 12 such that the temperature of electrode 12 maybe communicated to a processor or controller within the catheterassembly system to help control overall system operation and regulationof the irrigation fluid flow and ablation performed by the catheterassembly system. The configuration of thermal sensor 40 may be modifiedto work with various designs of open irrigation catheter assemblies.Moreover, more than one thermal sensor 40 may be provided in connectionwith an electrode. In embodiments in which a plurality of sensors 40 areprovided, the sensors may be used in combination to provide temperaturereadings associated with an electrode 12.

With reference to FIGS. 2 and 3, inner cavity 26 of electrode 12includes a central longitudinal axis 38 that extends along the length ofelectrode 12. Inner cavity 26 may have a generally tubularconfiguration, although alternate embodiments of the inner cavity arealso contemplated. In the illustrated embodiment, inner cavity 26extends through proximal portion 22 and into distal portion 24 ofelectrode 12.

As shown in FIGS. 2 and 3, an open irrigation electrode 12 includes atleast one fluid passageway 28—such as, without limitation, passageways28 a and/or 28 b shown in FIG. 2). Such passageway(s) 28 may include andbe referred to as conduit(s), irrigation port(s), irrigation hole(s),channel(s), or other types of structures employed by those of skill inthe art. In general, passageway 28 extends from internal cavity 26 to anouter surface 20 of electrode 12. Moreover, some open irrigationelectrodes, such as those illustrated in FIGS. 2 and 3, may include atleast one passageway 28 a that is perpendicular, or substantiallyperpendicular, to the central longitudinal axis 38 of electrode 12. Inaddition, as generally shown in FIG. 2, passageway 28 b may be providedthat extends along central longitudinal axis 38 from inner cavity 26 todistal end 36 to provide irrigation at distal portion 24 of electrode12.

In addition to those configurations reflected in FIGS. 2 and 3, variousalternative embodiments of fluid passageways may be incorporated withinelectrode 12, such as those described in currently pending applicationsassigned U.S. patent application Ser. Nos. 11/939,195 and 11/939,206,both of which are herein fully incorporated by reference. Furthermore,passageways 28 are disposed circumferentially around electrode 12. Inembodiments, the passageways may be provided so that they are generallyequidistant from one another, although alternate configurations andplacements of passageway 28 may be used depending on the design ordesired performance (e.g., to cover a given volume of fluid flow) ofelectrode 12.

Accordingly, the design of the passageways 28 may be modified to obtaina desired flow rate of the irrigation fluid based on a temperaturethreshold set by the overall system. The size and configuration ofpassageway 28 (such as 28 a and/or 28 b) may be varied depending on thesize and design of an associated electrode 12. In an embodiment, thediameter of passageway 28 may range from 10-20 thousandths of an inch.In another embodiment, the diameter of the passageway 28 may range from12-16 thousandths of an inch. Moreover, the flow rate and/or volume offluid flow may range from 13-20 ml/min. The diameter size of passageway28 may be configured to permit a given flow volume or rate, and furthermay be varied in connection with the number of passageways provided byelectrode 12, as well as the length of the electrode, or with otherfeatures associated with the electrode or catheter assemblies.

In addition to various passageway networks and configurations, electrode12 may include additional components, such as those typically used byablation electrodes, including but not limited to pressure sensors,power wires, or other features or components traditionally integratedwith catheter assemblies.

An open irrigation catheter assembly 12, such as generally describedabove, may be integrated into alternate embodiments of catheter assemblysystem 50 s, for example, as shown in FIGS. 4 and 5. System 50, 50′ maybe configured to control and regulate the flow of irrigation fluid suchthat the relative positioning of the electrode and establishment ofsufficient or improved physical contact is, at least in part,facilitated by a temperature feedback provided by electrode 12.

As generally shown in the embodiment illustrated in FIG. 4, catheterassembly 10 may be operably connected to a fluid source 52 (e.g., a pumpassembly) and an energy source 54 (e.g., an RF generator assembly),together comprising an embodiment of a catheter system 50. The fluidsource 52 and energy source 54 may serve to facilitate operation ofablation procedures and may involve monitoring any number of chosenvariables (e.g., temperature of ablation electrode, ablation energy,and/or position of the assembly), assisting in manipulation of theassembly during the use, and providing the requisite energy from asource that is delivered to the electrode 12. Furthermore, additionalcomponents may be integrated into the system. By way of example, withoutlimitation, such additional components may include visualization,mapping and navigation components known in the art, including St. JudeMedical, Inc.'s NavX® system or other related systems.

As generally represented in FIG. 4, fluid source 52 and energy source 54may be provided in combination with a catheter assembly 10 to comprise asystem 50. Fluid source 52 can comprise various known fluid sources,including fixed volume rolling pumps, variable volume syringe pumps, andvarious other pump assemblies known to those skilled in the art.Moreover, the fluid provided by fluid source 52, may comprise a suitablebiocompatible fluid, such as saline. The energy source 54 may comprise,for example and without limitation, an IBI-1500T RF Cardiac AblationGenerator available from Irvine Biomedical, Inc. The energy source canalso comprise various other known energy sources. In order to obtaincontrolled/regulated fluid flow within the system , energy source 54 mayalso, if desired, be configured with a temperature threshold setting andpump control switch (not shown). In an embodiment, energy source 54(i.e., generator) may monitor and detect the temperature of electrode 12of catheter assembly 10 and, once an established temperature thresholdis met, activate fluid source 52, therein either increasing/decreasingfluid flow or turning the pump completely on or off. Accordingly, FIG. 4generally illustrates a system having a closed control loop to controlthe flow of irrigation fluid, e.g., saline, based on the temperaturefeedback provided by catheter assembly 10.

FIG. 5 generally illustrates another embodiment of the invention whereinsystem 50′ integrates a controller 56, such as, for example, a computeror other type of processor or signal control device. Controller 56 maybe configured to receive input from energy source 54. Input received bycontroller 56 may further include temperature readings obtained fromcatheter assembly 10 (such as those provided in connection with athermal sensor 40 of electrode 12). Controller 56 can processtemperature readings and make comparisons/calculations with respect tospecified temperature threshold levels. Once a desired temperaturethreshold levels is established or obtained, controller 56 can output asignal to pump 52, which can in turn control irrigation fluid flowsupplied to catheter assembly 12. Continued (periodic or continuous)temperature readings from catheter assembly 10 may be provided tocontroller 56 and based on changes in the temperature readings ofcatheter assembly 10, controller 56 may modify its signal (e.g.,instructions) to pump 52, which can increase or decrease the associatedfluid flow. Various data, such as, for example, irrigation fluid flow(cc/min), temperature measurements, duration of fluid flow, andelectrode temperature response may be processed by controller 56. In anembodiment, controller 56 may also help assess (e.g., chart) variousdata or parameters, which may be reviewed by a user. Moreover, thesystem 50 can provide for dynamic assessment and review.

As represented in FIGS. 6-8, temperature readings of an electrode 10 ofcatheter assembly 12 and the provision of irrigation fluid have a directcorrelation with one another. As generally shown in FIG. 6, theconventional method of introducing irrigation fluid upon the onset ofthe ablation procedure results in the electrode temperature onlyreaching approximately 40 degrees Celsius. However, this can result inless effective ablation with respect to a target area and there may besome regulation difficulties if the ablation electrode is in directcontact with the target tissue. In comparison, FIGS. 7 and 8, withoutlimitation, illustrate delayed and intermitted irrigation, respectively,in accordance with embodiments of the present invention.

As generally shown in FIG. 7, irrigation fluid flow may initially bedelayed following application of ablation energy. The delay inirrigation fluid flow may either be obtained through a fixed delay or avariable delay. The fixed delay may occur, for example, when irrigationflow is delayed for a fixed or predetermined period of time, such as,for example, 10-30 seconds after the start of the ablation energy. Aftera fixed period of time has passed, the irrigation fluid may be providedto the catheter assembly. In contrast, a variable delay may occur, forexample, when irrigation flow is controlled by a predeterminedtemperature threshold. In a particular embodiment, the variable delaymay occur and continue until a temperature threshold level, e.g., 65degrees Celsius, is reached and then a constant irrigation fluid flowcan be provided and maintained for the duration of the ablationprocedure.

FIG. 8 illustrates an embodiment of an intermitted irrigation fluid flowand a correlation between irrigated fluid flow and resulting electrodetemperature response. The intermitted irrigation flow may occur foreither a fixed intermitted duration or for a variable intermittedduration. The fixed intermitted duration may, for example, occur for apredefined period of time, e.g., approximately 10-20 seconds, and thenreturn back to a maintenance flow level (e.g., 2 cc/min). This flowcontrol can occur for and throughout an entire ablation procedure. Inother embodiments, a variable intermitted duration may be controlled byan upper predetermined electrode temperature threshold level (e.g.,ranging from 50-70 degrees Celsius) and a lower predetermined electrodetemperature threshold level (e.g., ranging from 37-45 degrees Celsius).Accordingly, only a maintenance irrigation flow level may be initiallypresent (e.g., 2 cc/min), until an upper predetermined threshold levelis reached and then irrigation fluid flow may be initiated. Theirrigation fluid flow can be configured to continue until a lowerpredetermined electrode temperature threshold level is reached, at whichpoint the irrigation fluid flow may be decreased to return to amaintenance flow level. The foregoing can continue in the form of acycle or loop, which can result in an intermitted fluid flow throughoutan entire ablation procedure. Alternately, the irrigation flow may beturned off periodically during the ablation procedure to check thetemperature response of the electrode until the ablation is completely.

In accordance with the embodiments of the present invention, andperforming ablation of biological tissue through the use of openirrigated catheter assemblies, a temperature threshold may be preset inconnection with a generator 54. In embodiments, the temperaturethreshold level may range from 50-70 degrees Celsius, and for someembodiments may preferably be about 65 degrees Celsius. After atemperature threshold level is set or otherwise established, an openirrigated ablation catheter assembly 10 can be maneuvered to a targetlocation (such as, for example, the surface of the heart). Onceelectrode 12 of catheter assembly 10 is provided at a desired targetposition, energy can be applied by generator 54 to electrode 10.

The present invention further provides a method of irrigating biologicaltissue. The method can be initiated by providing an irrigated catheterablation system 50, 50′. The system 50, 50′ can include an irrigatedablation catheter assembly, a fluid source connected to the catheterassembly, an energy source connected to the catheter assembly, and anirrigation temperature control mechanism in communication with the fluidsource and energy source. The irrigated ablation catheter assembly 10may be in accordance with teachings previously described. The method mayinclude a step of establishing or presetting a temperature threshold forthe system that regulates irrigation fluid flow from the passageway ofthe catheter assembly. The irrigated electrode of the irrigated ablationcatheter assembly may be operatively positioned at a target location.Energy may then applied to the target location via an irrigatedelectrode. Temperature measurements associated with an electrode may becontinuously collected. The temperature measurements can be continuouslytaken by a thermal sensor disposed within an irrigated electrode. Aftereither a fixed period of time (fixed delay) or upon the temperaturemeasurement reaching a temperature threshold level (variable delay),irrigation flow may be initiated or increased (if an original (e.g.,maintenance flow was already present) to cool the electrode. Irrigationmay continue until ablation is discontinued. As previously described, anapplication of fixed delay irrigation may cause the irrigation flow tobe initiated, for example, about 10 to approximately 30 seconds afterthe application of the ablation energy was applied. In comparison, ifvariable delay irrigation is performed, the irrigation may be initiatedafter an upper temperature threshold level is reached, e.g., at about50-70 degrees Celsius.

Another embodiment further includes a method of irrigating biologicaltissue involving an intermitted irrigation flow. In addition to thesteps discussed above, additional temperature measurements of theirrigated electrode can be collected until a predetermined lowerthreshold is reached. Once a predetermined lower threshold level isreached, the irrigation flow may be discontinued. Temperatures cancontinued to be monitored and collected. If temperature measurementsreach an upper temperature threshold level again, irrigation flow can beinitiated or re-initiated, as the case may be. Such an intermittedirrigation cycle can continue until the ablation is formed. Alternately,the irrigation flow may be turned off periodically during the ablationprocedure to check the temperature response of the electrode until theablation is completely.

Although a number of embodiments of this invention have been describedabove with a certain degree of particularity, those skilled in the artcould make numerous alterations to the disclosed embodiments withoutdeparting from the spirit or scope of this invention. All directionalreferences (e.g., upper, lower, upward, downward, left, right, leftward,rightward, top, bottom, above, below, vertical, horizontal, clockwise,and counterclockwise) are only used for identification purposes to aidthe reader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Joinder references (e.g., attached, coupled, connected, andthe like) are to be construed broadly and may include intermediatemembers between a connection of elements and relative movement betweenelements. As such, joinder references do not necessarily infer that twoelements are directly connected and in fixed relation to each other. Itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not limiting. Changes in detail or structure may be made withoutdeparting from the spirit of the invention as defined in the appendedclaims.

1.-25. (canceled)
 26. An irrigated catheter ablation system comprising:an irrigated ablation catheter assembly including: an irrigatedelectrode, and a catheter shaft, wherein a distal end of the cathetershaft is coupled to a proximal portion of the irrigated electrode; afluid source fluidly coupled with the catheter assembly; an energysource electrically coupled with the catheter assembly; and anirrigation temperature control mechanism in communication with the fluidsource and the energy source, wherein the irrigation temperature controlmechanism is configured to control a flow rate of irrigation from thefluid source, and wherein the fluid source is configured to output afirst flow rate of irrigant, a second flow rate of irrigant, and a thirdflow rate of irrigant in response to the irrigation temperature controlmechanism.
 27. The system of claim 26, wherein the first flow rate ofirrigant is zero cc/min.
 28. The system of claim 26, wherein thetemperature control mechanism is configured to receive data relating toa temperature of the irrigated electrode.
 29. The system of claim 26,wherein the irrigated electrode comprises a thermal sensor and whereinthe temperature control mechanism is configured to receive data from thethermal sensor.
 30. The system of claim 29, wherein the thermal sensoris positioned within a distal portion of the irrigated electrode. 31.The system of claim 26, wherein the irrigated electrode comprises aplurality of thermal sensors and wherein the temperature controlmechanism is configured to receive data from the plurality of thermalsensors.
 32. The system of claim 26, wherein the flow rate output by thefluid source changes from the first flow rate to the second flow ratebased on a pre-set temperature threshold.
 33. The system of claim 26,wherein the flow rate output by the fluid source changes from the secondflow rate to the third flow rate based on a pre-set temperaturethreshold.
 34. The system of claim 26, wherein the flow rate output bythe fluid source changes from the third flow rate to the second flowrate based on a pre-set temperature threshold.
 35. The system of claim26, wherein the temperature sensor is positioned within the distalportion of the electrode.
 36. The system of claim 26, wherein theirrigation temperature control mechanism is coupled to the energysource.
 37. The system of claim 26, wherein the fluid source includes asaline pump.
 38. The system of claim 26, wherein the irrigationtemperature control mechanism includes a controller.
 39. A method ofirrigating biological tissue comprising: receiving information from anirrigated catheter ablation system, wherein the irrigated catheterablation system comprises an irrigated ablation catheter assembly, afluid source connected to the catheter assembly, an energy sourceconnected to the catheter assembly, wherein the information is receivedby an irrigation temperature control mechanism in communication with thefluid source and energy source, wherein the irrigated ablation catheterassembly includes a catheter shaft, and an irrigated electrode having aproximal portion coupled to a distal end of the catheter shaft;controlling a flow rate of an irrigation flow from the fluid sourcethrough the irrigated electrode, wherein the irrigation temperaturecontrol mechanism is configured to control the flow rate, and whereinthe fluid source is configured to output a first flow rate of irrigant,a second flow rate of irrigant, and a third flow rate of irrigant inresponse to the irrigation temperature control mechanism.
 40. The methodof claim 39, wherein the first flow rate of irrigant is zero cc/min. 41.The method of claim 39, wherein the irrigated electrode comprises athermal sensor and wherein the temperature control mechanism isconfigured to receive data from the thermal sensor.
 42. The method ofclaim 39, wherein the irrigated electrode comprises a plurality ofthermal sensors and wherein the temperature control mechanism isconfigured to receive data from the plurality of thermal sensors. 43.The method of claim 39, wherein the flow rate output by the fluid sourcechanges from the first flow rate to the second flow rate based on apre-set temperature threshold.
 44. The method of claim 39, wherein theflow rate output by the fluid source changes from the second flow rateto the third flow rate based on a pre-set temperature threshold.
 45. Themethod of claim 39, further comprising presetting or establishing atemperature threshold for the irrigated catheter ablation system thatregulates irrigation fluid flow from the passageway of the catheterassembly.